US2597535A

US2597535A - Radioactive assay apparatus

Info

Publication number: US2597535A
Application number: US685639A
Authority: US
Inventors: Emilio G Segre
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1946-07-23
Filing date: 1946-07-23
Publication date: 1952-05-20
Anticipated expiration: 1969-05-20

Description

M y 1952 E. G. SEGRE 2,597,535

RADIOACTIVE ASSAY APPARATUS Filed July 25, 1946 INVENTOR [MIL/0 6 $5 am:

y MZW ATTORNEY Patented May 20, 1952 RADIOACTIVE ASSAY APPARATUS Emilio G. Segre, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application July 23, 1946, Serial No. 685,639

1 Claim. 1

This invention relates to a fission assay apparatus in which a single source of neutrons is utilized to irradiate a plurality of fissionable samples.

The object of this invention is to provide fissionable sample assay apparatus employing a single source of neutrons adapted to be utilized for simultaneously irradiating a plurality of samples of fissionable material arranged in separate ionization chambers positioned around the neutron source.

Other and further objects of this invention will be apparent to those skilled in the art to which it relates from the following specification, claim and drawing.

Referring to the drawing briefly, the sole fi ure thereof illustrates an embodiment of this apparatus in a perspective view in fragmentary cross section.

The lead house in comprises a frame structure on which is supported a lead floor and a lead roof. Four pivoted doors H are respectively mounted on the sides of this structure. On each of the doors is mounted a lead panel l2. The lead floor, the lead roof, and the lead doors form a completely enclosed lead house. On the interior wall of each of the doors there is mounted an ionization chamber C and an associated amplifier A. A high voltage of a thousand volts is supplied to each of the ionization chambers from a common high voltage supply l3. The output of each of the amplifiers is connected respectively to a corresponding counter. The high voltage supply and the counters are disposed at a point of the laboratory remote from the lead house. Details of the circuits of the high voltage supply, the amplifiers, and the counters are described in the copending application of Clyde C. Wiegand, Serial No. 689,484, filed August 9, 1946 for Assay Apparatus, now abandoned. Within the lead house there is mounted a block of parafl'lne P or other substance adapted to absorb energy from fast neutrons. This block of paraffine includes cavities X into which the ionization chambers are adapted to fit when the doors are closed.

At the top of the lead house there is mounted a lead compartment M. This lead compartment is held in register with the center of the lead house by means of a brass tube which extends through an opening in the center of the roof of the lead house into a cylindrical cavity in the lower portion of the compartment. This brass tube fits within a cylindrical opening at the top of the parafiine block. The lower end of the brass tube terminates at about the center of the paraffine block and rests upon a copper disk R disposed at the bottom of the vertical cavity in the parafiine block. A source S of fast neutrons is arranged to be moved between an operative position at the bottom of this brass tube within the lead house and a safety position within the lead compartment. This source S comprises a brass capsule containing a radium-beryllium mixture enclosed by a covered copper can Y. Attached to the lid of the copper can is a rod [4 which extends through a vertical bore l5 passing through the upper end of the lead compartment. A cord l6 attached to the upper end of this rod passes over pulleys suitably supported in the roof of the assay room and terminates adjacent a hook on the wall of the assay room adjacent the interiors. By manipulation of the cord the source S may be lowered into its operative position within the lead house or raised to its safety position within compartment M. The source may be held in the safety position by tying the cord IE to the hook. The source emits gamma rays which are absorbed by the walls, the floor, and the roof of the lead house when the source is in its operating position with the doors closed and which are absorbed by the walls of the compartment when the source is in its safety position.

In practice, the source S is always retained in its safety position as long as any of the doors on the lead house is open and is moved to its operating position only when all of the doors are closed and an assay of one or more samples disposed within the respective ionization chambers C is to be performed. When the source is in its operated position, fast neutrons emitted therefrom are slowed up by the parafl'ine block P. Some of the resulting thermal neutrons are captured by the 235 component of a uranium sample mounted within the ionization chamber C. As a result, fission products are formed which cause the gas within the ionization chamber to be rendered conductive. Each of the resultant pulses produced actuates the corresponding counter. The number of such counts obtained in a measured time interval is utilized in connection with other measurements to determine the relative abundance of the isotopes contained in the uranium sample.

While I have described the salient features of this invention in detail with respect to one embodiment, it will of course be apparent that numerous modifications may be made within the spirit and scope of this invention and I do not desire therefore to limit the invention to the exact details shown except in so far as they may be defined in the following claim.

What is claimed is:

In apparatus of the character described, the combination comprising a shielded house defined by an apertured top wall, a bottom wall spaced therefrom and a plurality of intervening and interconnecting side walls provided with apertures and symmetrically disposed about a central axis normal to said first walls, a plurality of shielded doors for said second apertures mounted in said side walls equidistant from said axis and provided with fission chambers containing fissionable material, a hollow lead cylinder mounted on said apertured top wall above said house and provided with a tubular member fitting snugly within said cylinder and extending into said house through said apertured top wall along said axis, an apertured lead closure for one end of said cylinder and held in register therewith by studs substantially parallel with the longitudinal axis of said cylinder, a capsule containing radium and beryllium slidably positioned within said tubular member and having aifixed to one end thereof a rod extending through said apertured closure 4 whereby said capsule may be moved within said tube, and a neutron-decelerator comprising a body of paraffin disposed between said source and said fission chambers and having a source cavity located substantially on said axis and a plurality of fission chamber cavities disposed radially about said source cavity, there being substantially equal thicknesses of paraflin between said source cavity and each of said chamber cavities and substantially greater thicknesses of paraffin between any two of said chamber cavities.

EMILIO G. SEGRE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,206,634 Fermi et al July 2, 1940 2,287,620 Kallman et a1 June 23, 1942 2,306,194 Swaisgood Dec. 22, 1942 2,462,270 Lipson Feb. 22, 1949 2,477,648 Piggot et al. Aug. 2, 1949